The present invention relates generally to the field of mass storage systems and more particularly to the field of hard disk read/write head servo positioning systems.
The microcontroller in a modem hard disk system has many demands on its processing capabilities. As host computers demand quicker response, higher transfer speed, greater capacity, lower power, and other special features, the microcontroller is pushed to the limits of its capacity. Often, the microcontroller is forced to delay or deny one or more of these demands. This is especially true with the use of inexpensive microcontrollers to reduce disc drive costs.
One of the primary tasks of the microcontroller is that of guiding the hard disk's read/write head(s) across the disk platter(s), positioning the head in preparation for a read or write operation, and then to hold the head in place while the read or write operation is in progress. The more accurately the head can be moved into place, and centered over the location where the data is to be stored or read, the faster and more reliable the host computer will process its data; so the microcontroller must try to accomplish the move as fast and as accurately as possible.
First, to accommodate high transfer speeds, the platter is rotating at a very high speed. Thus, the microcontroller does not have much time in which to check the position of the head and make corrections. Alternatively, the speed which the platter rotates may be limited by the reaction time of the microcontroller. Second, to increase platter capacity, data is packed closer together on the platter. Thus, the read/write head must be positioned with optimum accuracy. Alternatively, the capacity of the disk drive may be limited by the precision of the positioning system. Third, in order to make the maximum amount of data storage space available, the number of servo bursts provided should be kept to a minimum. Also, if the head can be positioned more accurately, the tracks can be placed more closely together.
In short, the microcontroller in a modern disk drive system is asked to move the read/write head into position, and hold it in position, with fewer instructions, and with greater accuracy than ever before. There is thus a great need for a read/write head servo positioning system in which the above goals are achieved; this may be achieved, at least in part, by a system where some of these tasks are preformed independently of the microcontroller.